The present invention relates to an image forming apparatus comprising a corona discharging device provided at a predetermined interval from the surface of a photosensitive body and, more particularly, to an image forming apparatus such as an electrostatic copying apparatus or an electronic printer in which a corona discharging device is used for a charger, a transfer unit and a peeling unit.
In a copying machine which employs a photosensitive body formed of selenium or cadmium sulfide, corona discharging devices (corotron) are normally disposed as a charger, a transfer unit, a sheet peeling unit and a static eliminator at positions in the vicinity of the periphery of the photosensitive body.
On the other hand, copying machines of various types have been recently developed for practical use in which, in order to facilitate removing a paper jam in the periphery of a photosensitive body, any of these corona discharging devices could have been isolated from the periphery of the photosensitive body and then been returned to the original position after the paper jam has been cleared. One such device has been proposed in which a housing of the copying machine was divided into upper and lower units substantially at the boundary of a sheet conveying passage and the upper unit was rotatably pivoted with respect to the lower unit. In this copying machine, the photosensitive body was disposed in the upper unit and corona discharging devices were disposed as a transfer unit and a peeling unit in the lower unit. In this copying machine, the upper unit was rotatably displaced as required, thereby providing a wide interval between the photosensitive body and the corona discharging devices and accordingly simplifying the paper jam removing work.
However, the relative position between the photosensitive body and the corona discharging device has heretofore been defined by the contact between frames of the upper and lower units to each other. Accordingly, the relative position between the photosensitive body and the corona discharging device might not have been constantly defined due to irregularities in the dimensional and assembling accuracy at the time of manufacture. Further, when the upper unit has been repeatedly opened and closed, the pivotal position tended to shift slightly, with the result that the relative position between the photosensitive body and the corona discharging device might have varied. Thus, the conventional corona dischargers could not have stably performed corona discharge, causing improper transfer of an image or improper peeling of a sheet as its drawbacks.